1. Field of the Invention
The present invention relates to a fluid injector for x-ray tubes and a method to provide a liquid anode by liquid metal injection, with a device to inject fluid from an opening in a chamber of the device as a fluid jet generated by an arrangement to change the volume within the chamber, and comprising a reservoir to store the anode material, which is fluidically connected by a pipe with the chamber of the device.
2. Description of the Related Art
X-rays are used, for example, in clinical diagnostics and visualization. Usually, x-rays are generated by applying a high voltage to an x-ray tube. The x-ray tube is a capsulated device comprising vacuum and with an electron source, i.e., cathode as well with an electron target, i.e., anode.
Electrons emitted from the cathode are accelerated by an applied high voltage between anode and cathode, and hit the anode at a high velocity, i.e., energy. A high thermal load is generated at the anode material of the x-ray tube as an impact of the electron beam.
The interaction of electrons with anode material is accompanied by radiation, the so called “Bremsstrahlung” with a continuous spectrum and the “Characteristic” radiation with a discrete monochromatic spectrum. The “Bremsstrahlung” radiation spectrum is inefficient for various diagnostic applications in healthcare. Only some portion of the “Bremsstrahlung” radiation spectrum is used for quality imaging, while low energy photons overexpose the patient without contribution to the image quality. More than 99% of electron energy is converted into heat in the anode material, leading to a high amount of thermal load at the target material. This is especially the case when the x-ray focal spot is in the range of micrometers in diameter, to obtain high resolution x-ray images.
To reduce the thermal load at the anode, the target material can be changed rapidly in order not to accumulate the thermal load in a specific volume part of the target material. The most effective ways to provide rapidly changing anode material facing the electron beam are the use of rotating or moving solid state anodes, and another way is the use of a target formed by a flowing liquid material, such as a high Z material or a combination of a low and high Z material.
U.S. Pat. No. 3,836,805A, DE 3 429 799A1 and U.S. Pat. No. 6,735,283B2 disclose conventional x-ray cubes with rotating anodes are known from the state of the art. The limiting factor in the described arrangements is the maximum of rotational frequency, which is sensible to external acceleration for example of the whole tube, and it is difficult to fabricate tubes with a reliable transmission microfocus source.
U.S. Pat. No. 8,170,179B2, U.S. Pat. No. 7,929,667B1 and U.S. Pat. No. 7,412,032B2 also disclose conventional x-ray tubes with liquid metal in form of a jet used as anode are also known from the state of the art. The advantages of a liquid jet as a target material are the excellent heat transfer properties of liquid metals and the possibility to generate thin and fast liquid jets flowing free in vacuum or inside an electron- and x-ray transparent casing, such as with a jet with less than 0.1 mm diameter and more than 50 m/s velocity of the liquid flow. The disadvantage of the described arrangements is the use of complex recirculation systems, comprising pumps for high temperature liquid metal. The flow rate of liquid metal is limited by the pumps, the reliability of the arrangement is limited and pumps increase costs and complexity.